This invention relates to improvements in and relating to the production of composite metal tubing used for the manufacture of wedding bands, rings, and other tubular jewelry products, and more particularly to the manufacture of decorative metal objects which display a marbled, banded, or mosaic pattern on their surface produced by the novel lamination of multiple layers of two or more distinctly colored precious and, or non-precious metals.
Decorative metal techniques having a regular, random, or mosaic like patterns, such as the Japanese art of Mokume Gane (woodgrain metal), and the pattern welded steel (often times referred to as Damascus steel) of Japanese, Viking, and Middle Eastern smiths have been known for many years and continue to be used by today's artisans. These are processes for the welding and subsequent decorative pattern development of layers of contrasting colored metals or alloys and they have proven to be structurally and aesthetically superior to many other techniques such as inlay, overlay, double castings and solder bonding for both technical and aesthetic reasons. All of these methods aim to produce a composite material that displays colored patterns that are smooth and flush with the surface of an object, and one that is aesthetically pleasing, strong and durable.
The conventional methods of Mokume Gane, and Damascus Steel begin by preparing flat layers of contrasting colored metals or alloys and then welding them by various means into a large block or billet of composite metal. To expose the internal layers within the billet it is then taken through a number of labor intensive stages of selectively slicing, carving, twisting, forging, rolling, and forming to create intricate and aesthetically pleasing patterns on the surface of the wrought composite. After the desired pattern is imparted to the metal by these and other methods, the metal is then formed into an object of the makers design, such as a wedding ring. When forming a wedding ring, from such material, it is necessary to join the two ends of the rod or sheet that is used to create the ring so as to form a continuous, unbroken band. This seam is most often joined by soldering, by welding, or by cold connections such as rivets. Seamless rings may be made from this same material by machining the ring shape from a large block of the laminated composite metal.
A metal extrusion method has been disclosed in U.S. Pat. No. 3,171,195 issued to Darling. Darling discloses the bonding of multicolored metal components together to form a composite block, rod, or billet. The specific examples in the Darling patent disclose that one of the metals in the billet is in powder form, while the other(s) is (are) in a wrought form of wire, mesh, fragments, or shot. The two metals are placed in a container and the container is vibrated so that the powder is compacted around the other metal. The container, with the metals, is extruded so as to produce a billet of composite metal. After extrusion, the billet's internal patterning is exposed by serration machining, and then rolled into patterned metal strip to be used in fabricating various jewelry objects.
Other methods may be employed for the manufacture of metal products displaying decorative designs or patterns on their surface in two or more distinctly colored metals. For example, a regular or irregular patterned effect may be produced by machining or acid etching down into the surface of the metal and then filling these cavities with a metal or metals of a different color, from that of the metal base, so as to form an inlay in which the pattern or decorative inlay lies flush with the surface of the base. These inlays may be soldered in place, or mechanically held by undercutting the cavities in the base metal and forging the inlay metal into the cavity until it spreads out and conforms to the dimension of the cavity thereby binding it in place.
A further method consists in preparing composite metal rod or tube composed of two or more concentric tubes nested one within the other of differently colored metals, or alloys, intimately bonded to one another by drawing or extruding the rod, or tubing, in such a way as to metallurgically bond the individual tubes into one solid piece. The rod may be formed into a variety of jewelry objects, or rings such as wedding bands may be cut from tubing made by this method. The various colors of the metals used to create this composite tubing are exposed by further machining and selectively removing the top layer or layers of metal to reveal the contrasting layers below the original surface, and thereby create a decorative pattern.
Another method known as double casting consists of casting or machining a metal form to the desired size and shape to be utilized for the making of a jewelry or decorative object, which includes negative spaces within the form that takes the shape of the desired surface or inlay pattern. Metal of another color or alloy is then cast into these negative spaces creating a solid form that displays the desired surface pattern. A method very similar to double casting utilizes the same kind of cast or machined base that has been shaped to include negative spaces. These spaces are then filled with metal powder, which is compacted and sintered into place, thus achieving an appearance comparable to double casting.
Each of the above methods, however, suffers from certain inherent disadvantages, which renders it unsuitable or unsatisfactory for the economical production of finely patterned multicolored rings and other decorative metal objects, particularly objects such as wedding bands wherein the bonds between different metals must be strong enough to hold up to stretching and sizing as well as withstand decades of wear. Aesthetically these methods are also inferior in regards to producing a pattern with flowing, natural looking, or woodgrain patterns.
The traditional methods employed to create Mokume Gane and Damascus Steel cannot efficiently be utilized in a factory setting. Both of these methods are oriented to small-scale production by highly skilled artisans. Although these methods are capable of yielding very beautiful and finely patterned material, the knowledge, judgment, skill, and experience required to create this material is quite extensive and far beyond the expertise of factory workers. Additionally, because the material must be hand wrought, inconsistency of patterning and material integrity is quite common. Another drawback of material formed by other methods such as U.S. Pat. No. 3,465,419, U.S. Pat. No. 4,927,070, U.S. Pat. No. 4,399,611, U.S. Pat. No. 5,815,790, and U.S. Pat. No. 6,857,558 is that all are necessarily formed into, or utilize flat billets. These billets are then formed into patterned rod or sheet, which must then (in the example of wedding rings), be shaped into a circular ring form with a riveted, soldered, or welded seam. This degrades the ring in a number of ways.                1. The seam is an eyesore, which spoils the flow of the pattern in the composite metal ring.        2. The seam is a weak place in the ring and subject to breakage if the ring undergoes stress.        3. If it ever becomes necessary to re-size the wedding ring, the seam is vulnerable to breakage and its presence restricts the methods by which the ring may be successfully sized, making the whole process more labor intensive and expensive.        
Machining a seamless band from traditional patterned material also has severe disadvantages. When machining a ring from this material, it is necessary to cut away 80 to 90% of the material to create a ring shape. This is quite an inefficient use of the material, and when, in the case of wedding rings, the materials are precious metals, is cost prohibitive. Secondly, options for creating interesting patterns in thick billets of material that are large enough from which to machine rings, are severely limited, being simple variations of flat laminates.
The inlay process previously outlined is labor intensive, and requires skilled artisans trained in the method. These techniques are also beyond the skills of most factory workers and do not lend themselves to high volume production. In addition, soldered or hammer inlay techniques do not create a true metallurgical bond, so that the bonds created between the inlay and the base metal with these methods are forever vulnerable to separation. This creates many problems if the material has to be altered in shape, or forged, and in the case of wedding rings, makes sizing difficult and expensive. Lastly, inlay techniques by their very nature are quite coarse and cannot produce the fine sort of patterning possible by other methods.
The method utilizing concentric nested tubing (U.S. Pat. No. 4,114,398 and others) also has severe limitations. Because the tubing is axially straight walled, with the few layers of the composite tubing lying parallel to one another, patterning options are very limited and are, in a factory setting, constrained to cuts performed on a lathe or milling machine. By machining through the outer layers of tubing, different metals are exposed within the tube's core. This creates a simple pattern, but it is neither fine, nor does it yield a product where the design is flush to the smooth surface of the overall form. While this method can effectively mimic the appearance of difficult to produce metal overlay techniques, it is not suited for producing either fine or interesting patterns flush to the surface of a wedding ring, or other jewelry object. Also, because the cross sectional thickness of wedding bands made by this process varies widely, altering the finger size of these rings by conventional methods of stretching and rolling can be difficult.
The double casting method is also quite limited. The production of fine patterns in the base metal by casting is very difficult due to the delicateness required from both the wax models, and the metal castings. Also, the great variation in the thicknesses within the base metal piece, make casting these shapes difficult. Machining, etching, and stamping may also be used to create the cavities into which the inlay metal may be cast, but these methods are not capable of producing fine patterning of any substantive depth. This method also achieves no metallurgical bonding, and therefore the metal layers are prone to separate when any stress is applied to the object. The same holds true for the powder sintering method. While this method is superior to double casting in the sense that the inlay can achieve a diffusion bond with the cast or machined base, these bonds are still fragile and vulnerable to breaking in subsequent forming operations such as forging, rolling, or sizing.